I know its an old post but im experiencing exactly the same issue with my Macbook Pro Retina 2014 for few days.
I was at a Genius Bar this morning, he said me on this model we have to change everything because "all is linked together" (i bet that all is linked together, it's a computer you know, but come on...) and told me it will be a 650$ fix. I said no, i don't want to change the top-case/battery for now, and without it the price has well decreased, just 120$ to change the keyboard / trackpad. They kept my computer so I will give some news in few days to see what is going on.